In the prior art, composite materials are prepared by treating glass fiber preforms such as glass cloth, glass tape, glass mat, and glass paper and mica preforms serving as an inorganic reinforcement with organic resins such as epoxy resins, phenolic resins, polyimide resins and unsaturated polyester resins. These composite materials find use in a wide variety of applications. Laminates are often made of such composite materials. It is desired to improve the mechanical strength, electrical properties, water resistance, boiling water resistance, chemical resistance, and weatherability of such laminates. It was proposed to pretreat the inorganic reinforcements with silane coupling agents such as γ-aminopropyltriethoxysilane, β-aminoethyl-γ-aminopropyltrimethoxysilane, and γ-glycidoxypropyltrimethoxysilane, prior to the treatment with organic resins. This pretreatment enhances the adhesion of resins to the inorganic reinforcements.
Among others, those composite materials using phenolic resins as the organic resin have excellent heat resistance, dimensional stability and moldability and have long been used as the molding material in the basic industrial fields including automobiles, electric and electronic equipment. Under the recent trend aiming at reduced cost and weight, active attempts have been made to replace metal parts by high-strength molded parts of glass fiber-reinforced phenolic resins. In order to promote metal replacement in the future, the key is to achieve a high strength which has never been reached by prior art glass fiber-reinforced phenolic resin moldings. To achieve a high strength, many techniques of treating glass fibers with amino-silane coupling agents to enhance the adhesion to the matrix resin have been proposed. The treatment with coupling agents alone, however, encounters certain limits in enhancing strength. Under the circumstances, several techniques have been proposed for further improving the adhesion between glass fibers and matrix resins.
JP-A 52-12278 discloses that glass fibers to be admixed with a thermosetting resin are pretreated by applying a primer resin compatible with the thermosetting resin or a mixture of the primer resin and another primer agent such as a silane coupling agent closely to surfaces of glass fibers. It is described that high strength is achieved by dispersing the pretreated fibers in the thermosetting resin. This technique, however, exerts a rather little effect of enhancing the strength of molding material and is uneconomical because autoclave treatment is necessary at the stage when glass fibers are pretreated. For a diallyl phthalate polymer matrix, glass fibers pretreated with a diallyl phthalate polymer and a silane coupling agent are used. The disclosure thus refers to only the strength enhancement effect due to reaction and interaction between these diallyl phthalate resins, but nowhere to phenolic resin molding materials.
JP-A 10-7883 discloses a technique of producing a phenolic resin composition with improved rotational rupture strength by first sizing glass fibers with a phenolic resin of the same type as a matrix phenolic resin, then treating them with a coupling agent, and incorporating the treated glass fibers in a phenolic resin composition. With this technique, however, surfaces of glass fibers are directly treated with the phenolic resin. Since the phenolic resin generally has weak chemical bonding forces with glass fibers, a firm adhesion is not available between the fibers and the matrix resin. This technique is thus less effective in enhancing the strength of molding material.
In connection with the above technique, JP-A 2001-270974 discloses a technique of improving the mechanical strength of a phenolic resin composition at normal and elevated temperatures by treating glass fibers with a phenolic resin of the same type as a matrix phenolic resin and an amino-silane coupling agent at the same time, or treating with an amino-silane coupling agent and then with a phenolic resin of the same type as a matrix phenolic resin, and incorporating the treated fibers in a phenolic resin composition. The amino-silane coupling agent used herein has one or two primary amino and secondary amino groups per hydrolyzable silyl group. The degree of bond between the coupling agent with which glass fibers are treated and the phenolic resin is not sufficient. Then the coupling agent is regarded to be a factor of reducing the strength of the resin composition.